Key Points

• Growth hormone (GH) is indispensable for the attainment of adult stature.

• Growth hormone stimulates growth of the long bones by stimulating production of insulin-like growth factor I (IGF-I).

• Insulin-like growth factor I produced locally and in the liver stimulates growth and maturation of chondrocytes in epiphysial plates.

• Growth hormone increases lean body mass, decreases body fat, promotes fatty acid utilization, and limits carbohydrate utilization.

• Growth hormone is secreted in discrete pulses about every 3 hours, with the largest pulse occurring in the early phases of nocturnal sleep. GH is secreted throughout life; the highest blood levels are seen during adolescence and early adulthood and decline with increasing age.

• Growth hormone secretion is controlled by the hypothalamic GH-releasing hormone (GHRH), by the GH-release-inhibiting hormone somato-statin, and by IGF-I.

• Thyroid hormone is required by the somato-trope for normal GH synthesis and secretion. Thyroid hormones maintain tissue sensitivity to GH and IGF-I and hence are required for normal expression of GH actions.

• Optimal concentrations of insulin in blood are required to maintain normal growth during postnatal life.

Essential Medical Physiology, Third Edition

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